In the root directory of the ghc repository or source distribution, run either make fasttest, make test (which uses the normal speed settings) or make slowtest (called fulltest in GHC <= 7.10).
You should expect that there are no test case failures for the "normal" mode as that is a quality level that all GHC developers are expected to maintain when they check in code. There will usually be some test case failures for the full testsuite run though, and it takes a lot longer to run.
The run time of the testsuite can be reduced by running it with multiple threads. For instance if your machine has 8 cores, the following is probably appropriate: